VISION Flashcards
What pigment do rods use in the photoreceptor transduction cascade?
RHODopsin
What pigment do cones use in the photoreceptor transduction cascade?
Photopsin
Which vitamin is involved in rhodopsin synthesis?
vitamin A
what are the two molecules that form rhodopsin?
retinal (a.k.a retinaldehyde)
opsin
what is the difference between photopsin and rhodopsin?
There are 3 types of photopsin; I, II and III, all absorb different wavelengths of light
what is the light absorbing component of photopigments?
retinal
once retinal has absorbed light, which conformation will if be found in?
all TRANS retinal
what is the function of the opsin portion of the photopigment?
determines what wavelength of light is absorbed by retinal
binding of retinal
what wavelength of light is absorbed by rods?
498nm
what wavelength of light is abosrbed by red cone opsins?
564nm
what wavelength of light is absorbed by green cone opsins?
533nm
what wavelength of light is abosrbed by blue cone opsins
433nm
what in the structure of various opsin molecules determines which part of the light spectrum they will absorb?
amino acids that surround the retinal binding site
How do photoreceptors response to light exposure?
Graded hyperpolarisation e.g. if there is more light expsoure, there will be more hyperpolarisation
in the dark, how much glutamate do photoreceptors release into synapse with bipolar cells?
GLUTAMATE RELEASED IN ABUNDANCE
Glu is inhibitory at this stage
in the light, how much glutamate do photoreceptors release into the synapse with bipolar cells?
GLUTAMATE NOT RELEASED
Glu is inhibitory, therefore net excitation on post-synaptic bipolar cell
which photoreceptors are more sensitive to light?
Rods
what is the function of the horizontal cells?
provide antagonistic responses to photoreceptor activation via GABA @ outer plexiform layer
what is the function of amacrine cells?
Amacrine cells are inhibitory neurons, and they project their dendritic arbors onto the inner plexiform layer (IPL), they interact with retinal ganglion cells and/or bipolar cells
what is a ‘receptive field’ of a ganglion cell?
The area of the retina in which light absorption excites a single retinal ganglion cell
what is the ‘on-centre’ pathway?
pathway in which the synapse between a photoreceptor and bipolar cell is sign INVERTING i.e. glutamate in inhibitory to bipolar cell and pathway is excited when its light
what type of glutamate receptors are found in the on-centre pathway?
sign inverting metabotrophic glutamate receptors
what is the ‘off centre’ pathway?
pathway in which the synapse in the outer plexiform layer is sign CONSERVING i.e. glutmate is excitatory. Glu released in abundance when its dark, which excites off centre ganglion cells
what type of glutamate receptors are found in the off-centre pathway?
sign conserving ionotrophic glutamate receptors
what are the two continuums of colour axis differentiation?
Red - Green
Blue - Yellow
Cones of different colours side by side in receptive fields produce information on colour based on how inhibited/excited the central bipolar cell is
axons from which half of the RETINAL field decussate at the optic chiasm?
NASAL
axons from which half of the VISUAL field decussate at the optic chiasm?
TEMPORAL
where do fibres of the optic tract terminate?
lateral geniculate nucleus of thalamus
some fibres leave the optic tract and travel to the pre tectal nucleus. What are these fibres function?
afferent limb of pupillary reflex
what is the structure/function of baums loop?
division of the optic radiation
transmits information relating to the SUPERIOR retinal field
Travels via the parietal lobe
what is the structure/function of meyers loop?
division of the optic radiation
transmits information relating to the INFERIOR retinal field
Travels via the temporal lobe
a lesion that blocks the optic nerve of that eye, resulting in blindness in that eye….
Anopia
a lesion at the optic chiasm, causing temporal visual field defects in both eyes…
bitemporal hemianopia
what is the a common cause of bitemporal hemianopia?
pituitary adenoma
a lesion in the right/left optic tract, causing both nasal and temporal visual defects…
homonomous hemianopia
a lesion affecting meyers loop…
upper homonomous hemiquadrantanopia
a lesion effecting baums loop…
lower homonomous quadrantantopia
a lesion in the primary visual cortex…
homonomous hemianopia with central sparring
when light is in the centre of an ‘on centre’ cell, it is…
excited
when light is in the centre of an ‘off-centre’ cells, it is…
inhibited
via lateral inhibition of horizontal cells
when light is in the annulus/periphery of an on centre cell, it is…
inhibited
when light is in the annulus/periphery of an off centre cell, it is…
excited
what is myopia? how is it corrected?
shortsightedness- distant objects are blurred, near objects are seen clearly
corrected with concave lens
what is hypermetropia? how is it corrected?
longsightedness- both far and near objects are blurred
corrected with a convex lens
what is presbyopia? how is it corrected?
age-related longsightedness due to lens fibre deposition with age
convex lens correction
what is astigmatism? how is it corrected?
non-spherical curvature of the lens, meaning refraction isn’t equal throughout
corrected using a spherical lens
how is visual acuity tested?
snellen chart
a patient records a snellen chart fraction of 6/40. what does this mean?
6 - how far away the patient is (m)
40 - how far away the average person would be to read the symbols
what is the test for colour blindness?
ischihara test plates
how are visual fields tested?
confrontation testing
goldman perimeter testing
heterotropia, crossed eyes and squint are laymans terms for which visual condition?
Strabismus
what is the medical name for ‘lazy eye’?
amblyopia
